This application focuses on the role of CD81 in the cellular response of the retina to injury. This group was the first to demonstrate that CD81 is expressed in the retina and that there is a significant up-regulation of the gene product following injury. The hypotheses is that TAPA is part of the molecular complex mediating contact inhibition for glial cells and retinal pigment epithelium (RPE). This application will address four questions regarding CD81 and the proliferative response of retinal cells: (1) whether CD81 regulates glial cell and RPE number during normal retinal development; (2) whether CD81 plays a role following injury; (3) whether the activation of CD81 down-regulates the proliferative response of retinal glia; and (4) what glial proteins associate with CD81 to regulate cell proliferation in the retina.